Research And Realization Of The Image Capturing Embedded System Based On USB Webcamera

The process of designing a image-capturing system with a USB webcamera based on embedded system is described.This image-capturing system contains three modules:USB webcamera driver ,upper image-capturing module ,avi file-generating module .A webcamera driver which aims for USB webcamera chip zc301plh is designed.The frame rate of the driver is improved.There are three methods adopted in order to improve the webcamera driver's frame rate.Firstly,accordingly to the certain camera chip-zc301plh, the free spca5xx driver is trimmed reasonably.Secondly, double URB alternate circulation and double frames for buffering data and improving the V4L protocol are adopted in order to improve the performance of the designed driver.Thirdly,the USB webcamera driver we designed has mmap() system call but it has no read() system call . So the upper application applies for image by means of mmap() system call .Because mmap() system call could map the device memory spcace which belongs to kernel space to the user memory space,and therefore reduce the times of copying image data between the kernel space and the user space, improve the efficiency of image-capturing.The upper image-capturing programme which observes the improved video for linux standard.The improved video for linux standard follows:firstly,driver constantly captures images and buffers image data with double frame buffers,and sets flag which is used for marking'image already captured'when a frame image is captured;secondly, user mode programme can constantly grab images by giving only once'capturing image'request and waiting for the flag with blocking itself.The avi file-generating programme is designed .It can generate an avi video file based on many jpeg files captured by the system.Then the avi video file could be saved in the removed storage in order to implement the video replay.At last,the image-capturing system we designed can work stably under the condition of S3C2440A microprocessor and arm-linux operating system ,and it could achieve the intended goal.